Weiye Zhong

In Vivo Morphological Features of Human Lumbar Discs

AbstractRecent biomechanics studies have revealed distinct kinematic behavior of different lumbar segments. The mechanisms behind these segment-specific biomechanical features are unknown. This study investigated the in vivo geometric characteristics of human lumbar intervertebral discs.Magnetic resonance images of the lumbar spine of 41 young Chinese individuals were acquired. Disc geometry in the sagittal plane was measured for each subject, including the dimensions of the discs, nucleus pulposus (NP), and annulus fibrosus (AF). Segmental lordosis was also measured using the Cobb method.In general, the disc length increased from upper to lower lumbar levels, except that the L4/5 and L5/S1 discs had similar lengths. The L4/5 NP had a height of 8.6 ± 1.3 mm, which was significantly higher than all other levels (P < 0.05). The L5/S1 NP had a length of 21.6 ± 3.1 mm, which was significantly longer than all other levels (P < 0.05). At L4/5, the NP occupied 64.0% of the disc length, which was significantly less than the NP of the L5/S1 segment (72.4%) (P < 0.05). The anterior AF occupied 20.5% of the L4/5 disc length, which was significantly greater than that of the posterior AF (15.6%) (P < 0.05). At the L5/S1 segment, the anterior and posterior AFs were similar in length (14.1% and 13.6% of the disc, respectively). The height to length (H/L) ratio of the L4/5 NP was 0.45 ± 0.06, which was significantly greater than all other segments (P < 0.05). There was no correlation between the NP H/L ratio and lordosis.Although the lengths of the lower lumbar discs were similar, the geometry of the AF and NP showed segment-dependent properties. These data may provide insight into the understanding of segment-specific biomechanics in the lower lumbar spine. The data could also provide baseline knowledge for the development of segment-specific surgical treatments of lumbar diseases.

Sagittal plane rotation center of lower lumbar spine during a dynamic weight-lifting activity.

This study investigated the center of rotation (COR) of the intervertebral segments of the lower lumbar spine (L4-L5 and L5-S1 segments) in sagittal plane during a weight-lifting (3.6 kg in each hand) extension activity performed with the pelvis constrained. Seven healthy subjects were studied using a dual fluoroscopic imaging technique. Using the non-weightbearing, supine position during MRI scan as a reference, the average intervertebral flexion angles of the L4-L5 and L5-S1 were 6.6° and 5.3° at flexion position of the body, respectively, and were -1.8° and -3.5° at extension position of the body, respectively. The CORs of the lower lumbar spine were found segment-dependent and changed with the body postures. The CORs of the L4-L5 segment were at the location about 75% posterior from the anterior edge of the disc at flexion positions of the body, and moved to about 92% of the posterior portion of the disc at extension positions of the body. The CORs of the L5-S1 segment were at 95% posterior portion of the disc at flexion positions of the body, and moved outside of the posterior edge of the disc by about 12% of the disc length at extension positions of the body. These results could help understand the physiological motion characters of the lower lumbar spine. The data could also provide important insights for future improvement of artificial disc designs and surgical implantation of the discs that are aimed to reproduce normal spinal functions.

Anterior Lumbar Interbody Fusion for Degenerative Discogenic Low Back Pain: Evaluation of L4-S1 Fusion.

AbstractThe treatment of degenerative discogenic pain is controversial, and anterior lumbar fusion for the treatment of degenerative discogenic low back pain has also been a controversial topic for over a generation.The aim of this systematic review was to evaluate the outcome of different anterior lumbar fusion levels for degenerative discogenic low back pain.In this study, we performed a clinical outcome subgroup analysis. The outcomes of 84 consecutive patients who underwent anterior lumbar interbody fusion from 2004 to 2009 were reviewed. The operative time, intraoperative blood loss, hospital stay, Oswestry Disability Index (ODI), visual analog scale (VAS) results, and complication rate were recorded separately.Medical indications were degenerative disc disease (73.8%), postdiscectomy disc disease (16.1%), and disc herniation (9.5%). Patients with severe spondylolysis or disc degeneration, with more than 3 or multilevel lesions, were excluded.The mean operative time was 124.5 ± 10.9 min (range 51–248 min), the mean intraoperative blood loss was 242.1 ± 27.7 mL (range 50–2700 mL), the mean hospital stay was 3.9 ± 1.1 days (range 3–6 days), the mean preoperative VAS score was 7.5 ± 1.4, and the mean preoperative ODI score was 60.0 ± 5.7. At the 1-year follow-up, the mean postoperative VAS score was 3.3 ± 1.3 and the mean postoperative ODI score was 13.6 ± 3.4 (P < 0.05). L4–L5 disc fusion led to better clinical results than 2-level L4–L5/L5–S1 disc fusion. Additionally, the 2-level fusion of L4–L5/L5–S1 had better clinical results than the L5–S1 disc fusion at both the 1 and 2-year postoperative follow-ups regarding the VAS score and the ODI score. The rate of complications was more frequent in the 2-level L4–L5/L5–S1 group (27.3%) (group C) than in the L4–L5 group (9.1%) (group A) and the L5–S1 group (12.5%) (group B). There was no difference between the L4–L5 group (9.1%) and the L5–S1 group (12.5%). A venous tear occurred during surgery and was successfully repaired in 6 of the 84 patients. Also, out of the 84 patients, 6 were found with pseudarthrosis during the follow-up, and these patients underwent a spinal fusion with instrumentation, with a posterior approach after a mean of 1 year. The complications secondary to the surgical approach were persistent abdominal pain (1/84, 1.2%) and wound dehiscence (1/84, 1.2%).Anterior lumbar interbody fusion for L4–L5 had better clinical results than the 2-segmental L4–L5/L5–S1 disc fusion, and the 2-segmental L4–L5/L5–S1 disc fusion had better clinical results than the L5–S1 disc fusion. Also, the 2-segmental L4–L5/L5–S1 disc fusion had a higher complication rate (27.3%), but there was no difference between the L4–L5 group (9.1%) and the L5–S1 group (12.5%).

In vivo Characteristics of Non-degenerated Adjacent Segment Intervertebral Foramina in Patients with Degenerative Disc Disease during Flexion-Extension.

Study Design. In vivo patient biomechanical study. Objective. To investigate the dimensions of lumbar intervertebral foramen (LIVF) of patients with degenerative disc disease (DDD) during a flexion-extension motion of the body. Summary of Background Data. LIVF narrowing may result in nerve root compression. The area changes of degenerated and adjacent nondegenerated LIVFs in DDD patients under physiologic loading conditions are unknown. Methods. Nine symptomatic low back pain patients with radiological evidence of L4-S1 DDD were recruited. Each subject was magnetic resonance imaging scanned for construction of three-dimensional lumbar vertebral models, and fluoroscopically imaged when the body extended from 45 flexion to full extension for reconstruction of LIVF dimensions. The data of the adjacent segment L3/4 and diseased segments L4/5 and L5/S1 were compared with a normal control group at 45 flexion, upright, and full extension of the body. Results. The mean LIVF areas of DDD segments were significantly smaller than those of the normal subjects in all positions (P <0.05). In upright position, the LIVF areas of the DDD patients were 32.8% and 33.6% smaller than the normal subjects for L4/5 and L5/S1, respectively. For the adjacent L3/4, the LIVF area of the DDD patients was 32.3% smaller than that of the normal controls (P <0.05). The total change of L3/4 LIVF area in DDD patients from flexion to extension was significantly smaller than that of the normal subjects, but the changes in L4/5 and L5/S1 LIVF areas were similar between the two groups (P >0.05). Conclusion. Similar reductions of the LIVF dimensions were observed at the adjacent and the involved levels of the DDD patients, implying that biomechanical changes might have already occurred at the adjacent segment despite the lack of radiographic evidence of degeneration. Subsequent research should focus on the effects of surgical fusion on the biomechanical features of the adjacent segment. Level of Evidence: N/A